Free cutting steel containing mullite

ABSTRACT

A free cutting steel is disclosed having improved cutting properties which leads to improved service life for cutting tools. Th steel is characterized by the presence of a principal component of a nonmetallic inclusion contained within said steel existing essentially in the mullite region of three phase trigonometric diagram of the CaO-Al2O3-SiO2 system. The steel also contains 5 to 15 ppm calcium and 0.04 to 0.15 percent sulfur as elements which enhance the cutting properties of said steel. This steel exhibits excellent cutting properties both at high speed cutting using a cemented carbide tool (a super-hard cutting tool) and at low speed cutting using a tool of a high speed steel.

United States Patent 1 Yamakoshi et al.

[ Oct. 29, 1974 FREE CUTTING STEEL CONTAINING MULLITE [75] Inventors: Noboru Yamakoshi, Kobe; Tsugio Kaneda, Akashi; Yoshichica Yanagi; Kiichi Narita; Tatsu Fujita, Kobe,

all of Japan [73] Assignee: Kobe Steel, Limited, Kobe, Japan [22] Filed: May 10, 1973 211 Appl. No.: 359,024

[30] Foreign Application Priority Data May 10, 1972 Japan 47-46141 [52] U.S. Cl. 75/123 G, 75/123 L, 75/126 G, 75/128 E, 75/128 P [51] Int. Cl. C22c 37/00 [58] Field of Search 75/123 G, 126 G, 126 L, 75/123 L, 128 P, 128 E [56] References Cited UNITED STATES PATENTS 12/1971 Asada 75/123 R 1/1972 [to 3/1972 [to 75/123 L OTHER PUBLICATIONS Materials and Methods May-1957- pp. 247-248, Small Sulfar Addition Gives Better Tool Steel.

Primary Examiner-L. Dewayne Rutledge Assistant 'Examiner-Arthur J. Steiner 4 Attorney, Agent, or FirmOblon, Fisher, Spivak, McClelland & Maier [5 7 ABSTRACT A free cutting steel is disclosed having improved cutting properties which leads to improved service life for cutting tools. Th steel is characterized by the presence of a principal component of a nonmetallic inclusion contained within said steel existing essentially in the mullite region of three phase trigonometric diagram of the CaOAl O -SiO system. The steel also contains 5 to 15 ppm calcium and 0.04 to 0.15 percent sulfur as elements which enhance the cutting properties of said steel. This steel exhibits excellent cutting properties both at high speed cutting using a cemented carbide tool a super-hard cutting tool) and at low speed cutting using a tool of a high speed steel.

3 Claims, 14 Drawing Figures PAIENIEBw 29 m4 SHEET 1 BF 9 SiO FIG. 1

' ANORTHITE GEHLENITE CORUNDUM ANORTH ITE GEHLENITE CORUNDUM PAIENTEDnmzs x914 SHEET 2W 9 A I! currme CONDITIONS: 0.2 cunme TOOL- P10 -5.-5. 55 A 15 .15% 0.5mm) g CUTTING SPEED v= 3'50m/min. cunme DEPTH =1.5mm' E FEEDING RATE; (LZSmm/rev; E- DRY-TYPE g l l I CUTTING TIME (MIN) FIG.2

FATENTEDIJCT 2 9 I974 I SHEET 30F 9 -'5". 5, 3, I5". |'5' 05m CUTTING SPEED V=200m/min. CUTTING DEPTH I5mm CUTTING CONDITIONS:

CUTTING TOOL! PIO(-'5",

FEEDING RATE 0.25mm/rev. DRY- TYPE EV :53 53 x25 CUTTING TIME(miII.)

CUTTING CONDITIONS:

0. 25mm/rev. CUTTING DEPTH IBmm DRY-TYPE CUTTING TOOL! P1D('59-'55", 5", I5, I59, 05mm) CUTTING SPEED V=300m/min. FEEDING RATE CUTTING TIME (min) PAIENIEII'IIIII 29 I974 3.844.773 SIIEEI NM 9 CUTTING CONDITIONS:

03- CUTTING TOOL PIO(-'5I-'5,5, 5, I59 I59 05mm) Y CUTIING SPEED V= 3O0m/Inin. FEEDING RATE=0.2'5mm/rev I CUTTING DEPTH I5mm Z I DRY-TYPE x 75 I l3 0.2- v I 7 F I & I I Q I m I v E I 5 IX J I I I I I l '5 I0 I 6 CUTTING TIME (min) CUTTING commons: I

CUTTING TOOL: PIO(5.-5. 5,5 I5". I5", 05km) CUTTING SPEED V =250m/min FEEDING RATE =0.2'5mm/rey. 3 CUTTING DEPTH=I5mm DRY-TYPE E :30 X g E 20- x a Q5 r T ln- XX", /U' I O I I I I I 1 3 l0 I5 20 25 1) CUTTING TIME(min) PATENTEDum 29 m4 SHEET 8 or 9 c urrme CONDITIONS:

as 15D 53 v3:

CUTTING TIME (min.)

FIG. 8

PATENTEDIICT 29 I974 FLANK WEAR DEPTH V (min) OHOO- 3.844.773 SHEET 80F 9 CUTTING CONDITIONS! CUTTING TOOL 1 PI0(-5".-5,'5,51I5,|5% 05mm) CUTTING SPEED V 200m/min.

FEEDING RATE 0.25 mm/rev.

CUTTING DEPTH I5mm DRY-TYPE CUTTING mm...

FIG. 10

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to free cutting steel having improved cutting properties. More particularly it relates to sulfur-containing and calcium-deoxygenated free cutting steel containing nonmetallic inclusions of a specific composition and content. The sulfur and calcium contents of the steel are present in specific ranges.

2. Description of the Prior Art Heretofore, many approaches directed to the formation of calcium-deoxygenated, free cutting steel have been attempted and reported, since the discovery in 1960, by Professor H. Opitz of the Aachen Engineering College in West Germany that steel deoxygenated with a deoxidizer containing calcium possesses excellent cutting properties for cemented carbide tools.

Concerning the relationship of nonmetallic inclusions contained in steel as they relate to the cutting properties of the steel, Opitz suggested that nonmetallic inclusions essentially of gehlenite are particularly effective for enhancing the cutting properties of steel, in view of the fact that the melt-adhering matter on the edges of cemented carbide tools during the machining of steels having good cutting properties, is of a composition that falls within the gehlenite region of a trigonometric diagram of the CaOAl O SiO system. On the other hand, it has been reported in Japanese Patent Publications 8,340-68 and 29,657-71, that free cutting steels which contain nonmetallic inclusions consisting essentially of anorthite, which also appears in the trigonometric diagram of the CaOAl O SiO system, have good cutting properties.

It has been known that calcium-deoxygenated free cutting steels have highly improved cutting properties especially in high speed cutting applications using cemented carbide tools. However, there is little or no improvement in the cutting properties of tools derived from high speed steels under low speed cutting conditions. Thus, there is no difference in the cutting properties of tools derived from high speed steel used at low speeds and tools derived from common steel also used at low speeds.

In view of the differences between the cutting properties of high speed steel and common steels, attempts have been made as disclosed in Japanese Patent Publication 29,66l-7l to improve the cutting properties of calcium-deoxygenated, free cutting steel by adding to the steel such elements as S, Pb, and the like, which aid in the improvement of the cutting properties of steel under low speed cutting conditions. However, these attempts have not met with success.

A need, therefore, exists for a free cutting steel which can be used at both low and high cutting speeds with equal facility.

SUMMARY OF THE INVENTION Accordingly, one object of the invention is to provide a free cutting steel which possesses excellent cutting properties under both high and low speed cutting conditions.

Briefly, this and other objects of the invention as hereinafter will become readily apparent can be provided by a free cutting steel comprising a'steel deoxygenated by calcium which contains nonmetallic inclusions consisting essentially of a composition characterized by the mullite region of the trigonometric diagram of the CaO-AI O SiO system, wherein said steel also contains 5 to 15 ppm Ca and 0.04 to 0.l5% S.

BRIEF DESCRIPTION OF THE DRAWINGS A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

FIG. 1 is a trigonometric diagram of the CaO-Al- O SiO system illustrating the various nonmetallic compositions which may be incorporated as inclusions in steel which has been calcium-deoxygenated by combining a Fe-Si alloy and a Ca-Si alloy;

FIGS. 2 and 3 are plots showing the results of cutting tests (flank wear width) of cemented carbide tools which compares the cutting properties of tools of steel D of the present invention with comparative steels A FIG. 4 is a trigonometric diagram of the CaO-Al- O --SiO system showing the compositions of the nonmetallic inclusions contained in the steels of the present invention;

FIGS. 5 to 8 show the results of tests (crater wear depth and flank wear width) with cemented carbide tools which compare the cutting properties of the steels (E J steels; AISI 1,043 equivalent steels) of the present invention with those of a common steel, AISI 1,045 steel (Y steel) and a calcium-deoxygenated steel (2 steel) (equivalent to AISI 1,045 in which FIGS. 5 and 6 relate to high speed cutting conditions, while FIGS. 7 and 8 relate to low speed cutting conditions;

FIGS. 9 to 12 are plots showing the superb cutting properties of alloy steels (AISI 4,135 and 5,130 equivalent steels) of the present invention; and,

FIGS. 13 and 14 are plots comparing the cutting properties of the steels (H J) of the present invention with those of a common steel Y when tools of high speed steels are used.

DETAILED DESCRIPTION OF THE PREFERREDv EMBODIMENTS Experimental studies have been directed to the development of calcium-deoxygenated steels which possess improved cutting properties to which sulfur has been added in attempts to clarify the relationship between sulfur and the nonmetallic inclusions in the steels and the cutting properties of the steel. As a result, it has been found that calcium-deoxygenated free cutting steels containing nonmetallic inclusions of a specific composition and content, exhibit excellent cutting properties and that the sulfur added to the steel exerts a prominent effect on the cutting properties of the steel when it is used as a cemented carbide tool under high and low speed cutting conditions.

Suitable steels, which may be used in the present invention include low-medium carbon steels such as AISI 1,010 to 1,060 steels and low alloy steels containing at least one alloying element such as Mn, Ni, Cr, Mo, and the like, having the content shown below which includes steels of the AISI 4,000 series, 5,000 series, 6,000 series and 8,000 series:

Mn 0.30 to 1.5071 Cr up to 2.00% Mo up to 0.507: Ni up to 2.00%

Other suitable steels include fine grain low carbon or low alloy steels containing from 0.025 to 0.100 percent niobium.

To a melt of a steel which is essentially an SAE standard AlSl 1,020 steel containing an oxygen content of 0.01 to 0.04 percent were added an Fe-Si alloy and a Ca-Si alloy to deoxygenate the steel. After the alloys were added to the steel, F eS was added thereto to form nonmetallic inclusions within the steel of a composition which falls within the range of anorthite, gehlenite, corundum or mullite in the CaO--Al O --SiO ternary system. Table I shows when the various alloys are added and the amount of deoxidizer, Ca, and S present in the steel. The compositions of the nonmetallic inclusions are shown in the three phase diagram of the CaoA1 O -SiO system.

In Table l, the A C steels refer to those in which the Fe-Si alloy is charged in the last stage of convertor refining, followed by deoxidation with the Ca-Si alloy precharged in a ladle. Steel D, on the other hand, refers to a steel which is deoxygenated on a deoxidizer precharged ladle basis, i.e., the Ca-Si alloy is placed in the bottom of a ladle followed by the addition of Fe-Si, before pouring molten steel therein. Prior to the deoxygenation treatment, Fe-Mn alloy, or the like are added to the steel, as necessary, for the adjustment of the oxygen content in the molten steel as ,well as to adjust the composition thereof. Fe-Mn alloy can also be added to the melt at the time of deoxygenation. As can be seen from Table l and FIG. 1, the compositions of the nonmetallic inclusions are principally found in the anorthite region in the case of steel A, in the gehlenite region with steel B, in the gehlenite and corundum regions with steel C, and in the mullite region with steel D. FIGS. 2 and 3 show the test results of the cutting properties of cemented carbide tools fabricated from the four types of steels. As is clear from FIGS. 2 and 3, steel D of the present invention shows superior cutting properties in comparison to the other steels, A through To further substantiate the reproducibility of the results obtained for the calcium-deoxygenated steel (steel D) as well as for steels which have experienced the combined effects of calcium deoxygenation and the addition of sulfur, melts (0 content from 0.01 to 0.04 percent) of medium carbon steels such as the SAE standard steels AISl 1,035, 1,043, 1,055, and the like, and of low carbon steels such as AISI 4,135, 5,130 and the like are poured into ladles in which there has been placed 2.6 kg/ton of FeSi (25/75) and 1.25 kg/ton of CaSi (35/65) for the deoxygenation of the steels. FeS is added to each of said steels to achieve a sulfur content ranging from 0.04 to 0.10 percent. Table 11 shows the calcium content found in each portion of the ingots prepared and in the rolled steel products, in addition to the sulfur and niobium contents for each of the basic steels used which include AlSI 1,035, 1,043, 1,055, 4,135 and 5,130 steels. FIG. 4 shows the compositions of the nonmetallic inclusions contained in each portion of the ingots and the rolled bar steel products with the aid of the trigonometric diagram of the Cao-Al- O -SiO system.

As can be seen from Table I1 and FIG. 4, steels E through S of the present invention each have nonmetallic inclusions of compositions which are essentially encompassed by the mullite region of the ternary phase diagram wherein the calcium content ranges from 5 to 15 ppm (0.0005 to 0.0015 percent). More particularly, the test results which show the cutting properties of cemented carbide tools manufactured from steels of this invention under high speed cutting conditions are shown in FIGS. 5 to 8. In FIGS. 5 to 8, steel Y is a common AISl 1,045 steel which has been deoxygenated with Fe-Si alloy and aluminum without the addition of sulfur, and steel Z is a AlSI 1,045 steel which has been deoxygenated with calcium as in the cases of the H to J steels, with the omission of sulfur (nonmetallic inclusions are of compositions in the mullite region, Ca: 0.0012%, S: 0.02 percent). FIGS. 5 and 6 are plots illustrating the cutting properties of cemented carbide tools made from the steels shown under high speed cutting conditions (V300 m/min). Steels Hto J of the present invention exhibit superior cutting properties in comparison to steel Y, which is a common AISI 1,045 steel and in comparison to steel Z which has nonmetallic inclusions of a composition and a calcium content the same as those of the steels of the present invention, except that sulfur has not been incorporated in the steel. FIGS. 7 and 8 show the cutting properties of cemented carbide tools made from steels H, .I and Y under low speed cutting conditions (V=100 m/min). The steels H and J of the present invention exhibit excellent cutting properties, i.e., they are free of flank wear and crater wear, and thus are superior to steel Y which shows flank wear and crater wear. In addition, as sshown in FIGS. 9 to 12, the alloy steels-(A181 4,135 and h i TAEEE T1v T Steel s S content Nb content Ca content (Basic chemical Top portion Mid portion Bottom portion As-rolled composition) of ingot of ingot of ingot Rod E) 0.043 0.0008 0.0006 0.0013 0.0010 F) (A151 1035) 0.065 0.0007 0.0010 0.0011 0.0005 G) 0.0006 0.0013 0.0014 0.0010

TABLE ll-Continued Steels 5 content Nb content (11 content ('71) (Basic chemical ('1 (/1 Top portion Mid portion Bottom portion As-rolled composition) of lngot of ingot of ingot Rod 11 0.040 0.0009 0.0000 0.001 1 0.0013 11 0.000 0.0014 0.0007 0.001 1 0.0010 11 (AlSl 10431 0.109 0.0000 0.0000 0.0012 0.0007 Y) 0.020 Z 1 0.025 0.0008 0.0012 0.0014 0.001 1 K) 0.042 0.0000 0.0007 .001 1 00014 L 1 (AlSl 1055 0.001 0.0007 0.0000 0.0013 0.0010 M) 0098 0.0007 0.0009 0.001 1 0.0000

x) 0.015 N) (AlSl 4135) 0.043 0.074 0.0005 0.0007 0.00011 0.0007 0.007 0.0008 0.0008 0.0012 0.0007 P) 0.103 0.077 0.0007 0.0008 0.001 1 0.0000

w 0.025 01 SC1'22 0.042 0.045 0.0000 0.0009 0.001 1 0.0010 R1 (AISI 5130) 0.001 0.0005 0.0000 0.0012 0.00011 5) 0.1 0.047 0.0007 0.0007 0.0012 0.0010

. H n "mi N M equivalent steels) of the present invention exhibit supe- 0.04 may not yield the desired effects in the product rior cutting properties in comparison to steels X and W steels, while sulfur contents in excess of 0.15 percent to which sulfur has not been added in contrast to the will not yield steels having improved cutting properties carbon steels of the present invention. FIGS. 13 and 14 and results in steels having poor mechanical properties further show the superior cutting properties obtained such as toughness. in the case of steels containing niofor high speed cutting steels made from the steels of the bium, niobium should be present therein in the range present inventiOn- Specifically, G- 13 ShOWS he eof 0.025 to 0.1 percent to maintain a fine grain size, sults of test conducted with a lathe having a bit tool of while niobium contents greater than 0.100 percent will a high speed steel. The results show the superior liferesult in steels having poor cutting properties because times obtained for bit tools made from the cutting of the formation of carbides and/or nitrides of niobium. steels (H J) of the present invention in comparison to The carbon and silicon contents of the free cutting steel the lifetime obtained for the bit tool manufactured .range from 0.1 to 0.6 percent and 0.05 to 0.4 percent from common steel Y. Further, FIG. 14 shows that respectively. drills of high speed steels, when used in tests conducted H ving now f lly described the invention, it will be on a drilling machine, are capable of cutting for far apparent to one of ordinary skill in the art that many longer length h n Steels of the Present invenchanges and modifications can be made thereto withtion are used in comparison to Co m n Steel out departing from the spirit or scope of the invention As is apparent from the foregoing description, when as set f h h i the nonmetallic inclusions are limited to the mullite rewh i l i d as new d i d d to b Covered gions and when the calcium content is limited to the b L tt P t t i range from 5 to 15 pp calclumdeoxygenaled and l. A free cutting steel which contains 0.10 to 0.60 sulfur-containing free cutting steels are obtained which percent b 050 to 0.40 percent ili 04 to exhibit excellent cutting properties when sulfur is also 0.15 percent sulphur, and is calcium deoxygenated by present in the steel. the addition of 5 to 15 ppm calcium which forms non- The content of calcium should be limited to the range 4 metallic inclusions of a composition consisting essenfrom 5 to 15 ppm, because if the calcium content is less tially of the mullite region of a three phase trigonometthan 5 ppm, the intended deoxygenation effects can not ric diagram of the Ca0Al O -SiO system, whereby be achieved by the addition of calcium. On the other said free cutting steel exhibits superior cutting properhand, if the calcium content exceeds [5 ppm, then the ties because of the presence of said nonmetallic incluoxygen content of the steel will increase (naturally, fl Said Calcium and Said Sulfur thereinpart of the Ca is considered to exist in steel in the form free cuttmg steel of clalm r n Said fr f sy Th the Steel i lik l to hibi poor cuttmg steel further contains at least one alloy compochanical properties. In general, sulfur may be present Selected from the group Consisting of to in the steel as an impurity in a content in the neighbour- 150% PP to 200% P to 050% M0, and P hood of 0.03 percent. However, for the purposes of this to 200% invention, the sulfur content is specifically desired to The free F g steel of claim 1, Whefmald Steel be within the range from 0.04 to 0.15 percent based on further Contains (3-025 to 0100 Percent nloblumthe total amount of material. Sulfur contents less than UNITED STATES lA'll.-lN'l OFFICE CERTIFICATE OF CORRECTION Pa e 7 Dated October 29, 1974 Noboru Yamakoshi et al. Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

should read 0.05 to 0.40 percent silicon Signed and sealed this 4th day of February 1975.

(SEAL) Attest:

McCOY M. GIBSON JR. Attesting Officer C. MARSHALL DANN Commissioner of Patents FORM Po-mso uo-es) USCQMM-DC suave-P09 U.S, GOVERNMENT PRINTING OFFICE: 869- 9 

1. A FREE CUTTING STEEL WHICH CONTAINS 0.10 TO 0.60 PERCENT CARBOB, 0.50 TO 0.40 PERCENT SILICON, 0.04 TO 0.15 PERCENT SULPHUR, AND IS CALCIUM DEOXYGENATED BY THE ADDITION OF 5 TO 15 PPM CLACIUM WHICH FORMS NON-METALLIC INCLUSION OF A COMPOSITION CONSISTING ESSENTIALLY OF THE MULLITE REGION OF A THREE PHASE TRIGONOMETRIC DIAGRAM OF THE CAO-AL2O3-SIO2 SYSTEM, WHEREBY SAID FREE CUTTING STEEL EXHIBITS SUPERIOR CUTTING PROPERTIES BECOMES OF THE PRESENCE OF SAID NONMETALLIC INCLUSIONS, SAID CALCIUM AND SAID SULFUR THEREIN.
 2. The free cutting steel of claim 1, wherein said free cutting steel further contains at least one alloy component selected from the group consisting of 0.03 to 1.50% Mn, up to 2.00% Cr, up to 0.50% Mo, and up to 2.00% Ni.
 3. The free cutting steel of claim 1, wherein said steel further contains 0.025 to 0.100 percent niObium. 